Abstract: To study the characteristics and the generation mechanism of the secondary vibration, a theoretical model is built up and the dynamic equations are derived.Analysis results show that the structural secondary vibration is a resonance vibration of some components such as beams and floors, under the traffic-induced vibration excitation with a close dominant frequency to the components.Based on a real project, a 7-story frame structure, the internal secondary vibration reoccurred under different traffic vibrations excitated by elevated road, subway, and light railway, respectively, which validated the feasibility of the proposed theoretical model and the derivation of structural secondary vibration in this paper.